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Deploy complete NixOS system configurations to your homelab machines using the flake’s automatic discovery system.

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Overview

All NixOS configurations are stored in the systems/ directory. Each subdirectory with a default.nix file is automatically discovered and exposed as a nixosConfiguration.

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Understanding Flake References

The deployment commands use flake references in the format: 
.#<hostname>
Where:
  • . refers to the current directory (your flake root)
  • # separates the flake reference from the output attribute
  • <hostname> is the name of the directory in systems/

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Local Deployment

Deploy to the current machine you’re working on.
1

Navigate to repository

cd /path/to/homelab
2

Validate configuration

Always validate before deploying:
nix flake check
3

Deploy the system

sudo nixos-rebuild switch --flake .#<hostname>
Replace <hostname> with your system’s configuration name from systems/.
The switch command immediately activates the new configuration. Use boot instead if you want changes to apply only after reboot.

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Deployment Commands

Different deployment modes for various scenarios: 
# Build and activate immediately
sudo nixos-rebuild switch --flake .#<hostname>

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Remote Deployment

Deploy to a remote NixOS system over SSH.
1

Ensure SSH access

Verify you can SSH to the target system:
ssh root@<target-host>
Or configure SSH with appropriate user and sudo access.
2

Deploy remotely

nixos-rebuild switch --flake .#<hostname> --target-host root@<target-ip>
Or with a specific user:
nixos-rebuild switch --flake .#<hostname> \
  --target-host <user>@<target-ip> \
  --use-remote-sudo

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Building from Remote Host

For systems with limited resources, build on a more powerful machine: 
nixos-rebuild switch --flake .#<hostname> \
  --target-host root@<target-ip> \
  --build-host root@<build-server-ip>

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Dynamic Discovery

The flake automatically discovers all system configurations: 
nixosConfigurations = lib.mapAttrs mkSystem (lib.discover ./systems);
Any directory in systems/ containing default.nix is automatically available for deployment.

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System Configuration Structure

Each system directory should contain: 
systems/<hostname>/
├── default.nix      # Main configuration
├── hardware.nix     # Hardware-specific settings (optional)
├── meta.nix         # Metadata (system architecture, etc.)
└── ...              # Additional modules

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Rollback and Recovery

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Rollback to Previous Generation

If a deployment causes issues: 
sudo nixos-rebuild switch --rollback

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List Available Generations

sudo nix-env --list-generations --profile /nix/var/nix/profiles/system

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Switch to Specific Generation

sudo /nix/var/nix/profiles/system-<number>-link/bin/switch-to-configuration switch

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Home Manager Integration

Systems automatically include Home Manager configurations for users. The system will look for:
  • homes/<user> - Base user configuration
  • homes/<user>@<hostname> - Machine-specific overrides
These are integrated automatically and deployed with the system.

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Troubleshooting

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Build Failures

If the build fails:
  1. Check validation output: nix flake check
  2. Review error messages for missing options or syntax errors
  3. Verify all required inputs are accessible
  4. Check disk space: df -h /nix

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Activation Failures

If activation fails after successful build:
  1. System remains on previous generation (safe)
  2. Check systemd journal: journalctl -xe
  3. Review activation script output
  4. Test configuration: nixos-rebuild test --flake .#<hostname>

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SSH Deployment Issues

  • Verify SSH key authentication is configured
  • Check firewall rules on target system
  • Ensure Nix is installed on target system
  • Verify network connectivity

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Advanced Options

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Updating Flake Inputs

Update all dependencies before deploying: 
nix flake update
sudo nixos-rebuild switch --flake .#<hostname>

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Update Specific Input

nix flake lock --update-input nixpkgs-weekly

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Show Configuration Diff

See what will change: 
nixos-rebuild build --flake .#<hostname>
nvd diff /run/current-system ./result

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Best Practices

Always run nix flake check before deploying to production systems. This validates all configurations and prevents failed deployments.
  • Test changes on non-critical systems first
  • Keep your flake inputs updated regularly
  • Document custom configurations in comments
  • Use nixos-rebuild boot for major changes
  • Maintain backup configurations
  • Version control all changes with git

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Next Steps

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